(a) Technical Field
The present invention generally relates to a composite sound absorbing material for a vehicle and a method for manufacturing the same, and more particularly, to a composite sound absorbing material and method of manufacture which improves a sound absorption coefficient of a low-to-mid frequency region and which is lightweight.
(b) Background Art
Recently, in order to improve customer satisfaction, car manufacturers have been addressing the issue of vehicle noise reduction. Accordingly, the reduced level of noise in a vehicle has been used in marketing a vehicle brand.
Improvement of sound absorption/transmission performance is closely related to quality, weight, and thickness of a sound absorbing/transmitting material. Conventionally, in order to reduce vehicle noise, the weight and thickness of the sound absorbing/transmitting material has been increased. However, but such a solution is limited due to fuel efficiency and limited space within the vehicle.
Hence, a porous sound absorbing material, such as glass wool, resin felt, polyethylene terephthalate (PET) felt, or the like, has been used. These materials are useful in terms of sound absorbing performance in a high-frequency region by increasing their thickness and weight. However, such materials cannot provide improvement for noise in a low-to-mid frequency region of 2 kHz or less.
Thus, composite sound absorbing/transmitting materials manufactured by stacking and combining various types of sound absorbing materials and sound transmitting materials have been used together with porous sound absorbing materials.
A conventional composite sound absorbing/transmitting material is in the form of a composite layer in which a sound absorbing material having a porous structure and a sound transmitting material having a non-ventilation structure are stacked. For example, as shown in FIGS. 5A through 5C, the composite sound absorbing/transmitting material may have a form in which skin nonwoven fabric, polyurethane (PU) foam, and skin nonwoven fabric are stacked; a form in which skin nonwoven fabric, resin felt, and rubber are stacked; or a form in which PU foam, rubber, and PET felt are stacked.
Such conventional composite sound absorbing/transmitting materials may be applied to, for example, a hood insulator, a dash insulator, and a dash iso pad of a vehicle.
However, these conventional composite sound absorbing/transmitting materials which utilize a rubber type of sound transmitting material have increased weight (see, e.g., FIGS. 5B, 5C), and when they do not include the rubber type of sound transmitting material (see, e.g., FIG. 5A), they have increased thickness which results in weight increase.